Gas Laws 14.4

Dalton’s Law• The contribution each gas in a mixture makes to the

total pressure is called the partial pressure exerted by that gas.

Dalton’s Law

– In a mixture of gases, the total pressure is the sum of the partial pressures of the gases.

Dalton’s Law• Dalton’s law of partial pressures states that, at

constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

Dalton’s Law• Three gases are combined in container T.

Dalton’s Law• The partial pressure of oxygen must be 10.67 kPa or

higher to support respiration in humans. The climber below needs an oxygen mask and a cylinder of compressed oxygen to survive.

Graham’s Law• Graham’s Law– How does the molar mass of a gas affect the

rate at which the gas effuses or diffuses?

Graham’s Law• Diffusion is the tendency of molecules to move toward

areas of lower concentration until the concentration is uniform throughout.

Graham’s Law• Bromine vapor is

diffusing upward through the air in a graduated cylinder.

Graham’s Law• After several hours,

the bromine has diffused almost to the top of the cylinder.

Graham’s Law

• During effusion, a gas escapes through a tiny hole in its container. –Gases of lower molar mass diffuse and

effuse faster than gases of higher molar mass.

Graham’s Law

– Thomas Graham’s Contribution• Graham’s law of effusion states that the rate of

effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

Graham’s Law

– Comparing Effusion Rates• A helium filled balloon will deflate sooner than an air-

filled balloon.

Graham’s Law• Because the rate of effusion is related only to a

particle’s speed, Graham’s law can be written as follows for two gases, A and B. (The gas with the least mass should be A)

Graham’s Law• Helium effuses (and diffuses) nearly three times faster

than nitrogen at the same temperature.